Drink More Water. Here's Why

Q. Why does my doctor want me to drink so much water?

A. Water, the most abundant substance in the body, is an essential component of all tissues. Everyone loses about 68 ounces of water a day, mostly through perspiration and urination. This water must be replaced to prevent excessive loss (dehydration). Persistent, unreplaced water loss of about 80 ounces daily can cause muscle weakness, fatigue, dizziness, headaches, confusion, forgetfulness, or an elevated heart rate. Dehydration is one of the most frequent causes of hospitalization after age 65.

Thirst indicates that you should drink. Because the sensation dissipates long before all water is replaced, however, it’s not a reliable indicator of the need for water especially in older people, who tend to have a reduced sense of thirst. Urine concentration also indicates fluid status. Darkly colored urine is often too concentrated and suggests dehydration; clear urine is usually diluted, suggesting adequate fluid intake.

The general recommendation to drink at least six to eight 8-ounce glasses of water daily can be accomplished by drinking water as well as other fluids (broth and fruit juice) and by eating foods that contain a large percentage of water (fruits, vegetables and soups). Caffeinated and alcoholic beverages are less helpful because they promote water excretion.

You may need more water when you exercise, if the weather is unusually hot or cold, or if you have certain medical problems (including respiratory infections or diarrhea).